The PutA protein from Salmonella is a complex multifunctional protein that functions as a flavin dehydrogenase when associated with the membrane and as a transcriptional repressor when located in the cytoplasm. In addition, PutA is autophosphorylated on serine, threonine, and tyrosine residues in vivo and in vitro. PutA protein contains many serine, threonine, and tyrosine residues, and the positions of the serine, threonine, and tyrosine residues that are phosphorylated is unknown. Furthermore, although a model has been proposed that phosphorylation limits the toxic accumulation of excess PutA in the membrane, because it has been impossible to directly test this hypothesis, the function of PutA autophosphorylation is unknown. The primary goals of this research are to identify the sites within PutA that are phosphorylated, to construct mutations that alter phosphorylation of these sites, and to determine the effect of these mutations on each of the functions of PutA. In addition, this research will define the functional domains of PutA protein. These studies may reveal mechanisms used to coordinate the expression and activity of important peripheral membrane proteins in response to the availability of membrane-binding sites.